The present invention relates to a positioning and clamping apparatus that positions and fixes in a predetermined position a member to be fixed such as a panel constituting a vehicle body.
Vehicle bodies are manufactured by joining a plurality of panels by means of welding means such as spot welding. In the case of welding thin iron plates, such as panels constituting the vehicle body, it is necessary to position these panels in predetermined positions and clamp the panels. Conventionally, a clamping device as described in, for example, Japanese Patent Laid-Open Publication (JP-A) No. 9-144715 has been used.
This clamping device uses air pressure as a driving force for driving a clamp arm, and in addition to the air pressure piping for supplying compressed air into a pneumatic cylinder, an electric wiring is provided with respect to a sensor for detecting that a piston is in a predetermined position. Therefore, it is necessary to let the air pressure piping and the electric wiring creep about the clamping device. In particular, when panels constituting the vehicle body are fixed, it is necessary to use a multiplicity of clamping devices for fixing one panel, and to let the air pressure piping and the electric wiring creep about the clamping device in a complicated manner.
On the other hand, it has been studied to use an electric motor as a driving force for the clamp arm. However, in case that a screw member is axially moved by the motor and that this axial motion is converted into the opening/closing motion of the clamp arm to thereby operate the clamp arm, the current value of the motor should be detected or a load applied on the motor should be detected, using a load cell, in order to prevent overloading of the clamp arm from occurring, by controlling the ON/OFF of the motor. Accordingly, a loop control having a feedback function must be employed as a control system of the motor, and as a result, the clamping device becomes expensive.
If the control of the motor which opens/closes the clamp arm can be performed by an open loop control, it becomes possible to open/close the clamp arm by a low-cost motor including a control section.
It is an object of the present invention to make it possible to reliably perform positioning and clamping of a member to be fixed, and unclamping thereof by a low-cost motor.
According to a first aspect of the present invention, there is provided a positioning and clamping apparatus comprising: a support barrel having a supporting face formed thereon for supporting a member to be fixed and provided with a positioning pin to which a positioning hole formed on the member to be fixed is fitted; a clam arm mounted in a slit formed in the positioning pin so as to be able to swing and so as to be able to move axially in an advancing/retreating direction, and having a clamp jaw provided at a tip thereof for clamping the member to be fixed between the supporting face and the clamp jaw; a drive housing mounted to a rear end portion of the support barrel, and having a reciprocating shaft connected to the clamp arm so as to be able axially reciprocate; a spring member provided in the drive housing, for applying a spring force to the clamp arm in a retreating direction via the reciprocating shaft; a plunger mounted in the drive housing so as to be able to reciprocate and brought into contact with the reciprocating shaft; and a motor mounted to a rear end portion of the drive housing and provided with a rotor connected in a threading manner to a male screw member secured on the plunger.
According to a second aspect of the invention, a retreating stroke end of the plunger is set to be rearward of a retreating stroke end of the reciprocating shaft. Also, according to a third aspect of the invention, a female screw is formed on a hollow rotation shaft provided in the motor, and the male screw member is connected to the rotation shaft in a threading manner. Furthermore, according to a fourth aspect of the invention, the male screw transmits a rotating motion of the rotor in the axial direction of the male screw member, and has a lead angle such that the rotor is not rotated by an axial thrust of the male screw member.
According to the present invention, when positioning and clamping of a member to be fixed is performed by a motor, the member to be fixed is clamped by a spring force, at the time of clamping. Therefore, clamping or unclamping of the member to be fixed can be performed, using a small motor as a driving force, without causing overloading of the clamp arm. The length of the device can be also made short, by making the rotation shaft of the motor a hollow shaft. The length of the device can be made shorter, by providing a female screw in the hollow shaft, which is thread-connected to the male screw member, enabling achievement of a small device. Moreover, the plunger is thread-connected to the rotor via the male screw member, in such a manner that the male screw member moves axially only when the rotor rotates, and even if an axial thrust is applied to the male screw member, rotation of the rotor can be prevented.